How to make half square triangles was shown to us by Marlene Dunlap. The easy angle ruler and companion angle ruler were used together. This method wastes nothing.
There are many videos on line to explain how to use the easy angle ruler, here are two:
https://www.youtube.com/watch?v=ll7yDcsbBDk
https://www.youtube.com/watch?v=eSwJJVqGom